This invention relates generally to a stereoscopic image display device which displays an image from a plurality of points of view with a stereoscopic vision, and more particularly to a stereoscopic image display device which converges spatially modulated light of left and right images having binocular parallax on the vicinities of the corresponding left and right eyes of a viewer to make the viewer recognize a stereoscopic image.
Recently, stereoscopic image display devices which use images having binocular parallax to make a viewer recognize them as a stereoscopic image are reported. Among them, attention has been paid to stereoscopic image display systems which do not require special spectacles since viewers can easily enjoy stereoscopic images.
Jpn. Pat. Appln. KOKAI Pub. No. 6-225344 discloses such a stereoscopic image display system which displays images while following the motion of a viewer, without requiring special spectacles. In this system, back-light for left and right sides is emitted through a large-sized convex lens to the position, or thereabouts, of the viewer's face or the viewer's left or right eyes. Therefore, since the position of light sources of back-light change as the viewer moves, a good tracking is achieved.
However, in this conventional art, as the viewer moves leftwards or rightwards from the front position, an angle .phi. formed between the light axis of incident light passing through the spatial modulation element and the surface of a liquid crystal board used as the spatial modulation element increases, and the amount of an orthogonal-projection component of incident light reduces. Further, in this conventional art, a black-and-white television wherein a phosphor-coated surface is used as a luminous member is used. The luminescent section of this light source can be regarded as a perfect diffusion light source whose luminance is uniform even if it is viewed from any angle. When the luminous intensity in the vertical direction is Io, the luminous intensity in the oblique direction is Io cos .phi.. Therefore, the luminous intensity has such characteristics that the luminous intensity reduces according to the degree of obliqueness of the direction in which the light source is viewed. Further, the liquid crystal board used as the spatial modulation element has such general characteristics that its transmissivity lowers when the light incident direction shifts from the vertical axis.
As explained above, in the conventional stereoscopic image display device, there were the problems that the image to be viewed becomes dim as the viewer moves leftwards or rightwards from the central position, and that the stereoscopically viewable region is narrow. Further, even when the viewer does not move, a peripheral portion of an image to be viewed is dimmer than a central portion.